The present invention, in some embodiments thereof, relates to Computer Generated Holograms (CGHs) and, more particularly, but not exclusively, to methods and apparatus for despeckling CGHs.
CGHs may be produced by projecting coherent light onto computer controlled Spatial Light Modulators (SLMs). The SLMs include an array of light modulators which are programmed by a computer to modulate light, so that light coming off the SLM (passing through or reflected off the SLM) produces a hologram.
Background art includes:
PCT Published Patent Application WO 2010/004563 by Rotschild et al, which discloses methods and systems for displaying images, and for implementing volumetric user interfaces. One exemplary embodiment provides a system comprising: a light source; an image producing unit, which produces an image upon interaction with light approaching the image producing unit from the light source; an eyepiece; and a mirror, directing light from the image to a surface of the eyepiece, wherein the surface has a shape of a solid of revolution formed by revolving a planar curve at least 180° around an axis of revolution. Another exemplary embodiment provides a method for implementing a floating-in-the-air user interface, including displaying a first image in a display space of a first floating-in-the-air display, inserting a real object into the display space of the first floating-in-the-air display, locating a location of the real object within the display space of the first floating-in-the-air display, locating the real object in the display space, and providing the location as input to the floating-in-the-air user interface;
PCT Published Patent Application WO 2012033174 titled “ILLUMINATION APPARATUS, PROJECTION APPARATUS, AND PROJECTION VIDEO DISPLAY APPARATUS”;
U.S. Published Patent Application 2011/0176190, which describes a method for reconstructing a holographic projection comprising providing a single hologram, providing at least one cyclic shift of at least a portion of the single hologram in the space domain, and reconstructing a cyclically shifted hologram by applying said cyclic shift on said portion;
U.S. Published Patent Application 2011/002019, titled “HOLOGRAPHIC IMAGE DISPLAY SYSTEMS”, describes an invention which relates to techniques for speckle reduction in holographic optical systems, in particular holographic image display systems. We describe a holographic image display system for displaying an image holographically on a display surface, the system including: a spatial light modulator (SLM) to display a hologram; a light source to illuminate said displayed hologram; projection optics to project light from said illuminated displayed hologram onto said display surface to form a holographically generated two-dimensional image, said projection optics being configured to form, at an intermediate image surface, an intermediate two-dimensional image corresponding to said holographically generated image; a diffuser located at said intermediate image surface; and an actuator mechanically coupled to said diffuser to, in operation, move said diffuser to randomize phases over pixels of said intermediate image to reduce speckle in an image displayed by the system;
U.S. Published Patent Application 2010/194745, titled “Holographic Display Having Improved Reconstruction Quality”, discloses is a display for the holographic reconstruction of a three-dimensional scene using means which allow a reduction of speckle patterns. Speckle patterns result in the graining of a holographic reconstruction and worsen the quality thereof. The 3D scene is incoherently superimposed with itself chronologically or spatially in the eye of the observer. The modulated wave fronts of each reconstructed object point of the scene are shifted relative to themselves in the reconstruction beam path and superimposed in the eye of the observer. The shifting may occur one-dimensionally and two-dimensionally. Each object point is multiplied with itself in the eye of the observer in accordance with the number of the shifted wave fronts. The various speckle patterns over which the eye of the observer averages are also multiplied. Speckle patterns are reduced and the reconstruction quality is thus increased in holographic displays;
U.S. Published Patent Application 2010/0097672, which describes a method for reducing speckle patterns of a three-dimensional holographic reconstruction. A controllable light modulator into which a three-dimensional scene is coded is illuminated by coherent light, a reconstruction means projects the modulated light close to an eye position into a space of observation and a control means controls the illumination. This provides a holographic reproduction device in which the speckle patterns occurring during reconstruction of a three-dimensional scene are reduced. Also provided is a next-to-real time method using a carrier medium of conventional image refresh rate;
U.S. Published Patent Application No. 2009/296176 titled “Method and Device for Reducing Speckle” describes a method for reducing speckle patterns of a three-dimensional holographic reconstruction is disclosed. A controllable light modulator into which a hologram of a three-dimensional scene is coded is illuminated by coherent light, a reconstruction lens transforms the modulated light into an eye position and reconstructs the three-dimensional scene in a reconstruction space and a control means controls the illumination. This provides a holographic reproduction device in which the speckle patterns occurring during reconstruction of a three-dimensional scene are reduced. According to one embodiment, a next-to-real time method is presented using a carrier medium of conventional image refresh rate;
U.S. Published Patent Application No. 2009/0040527 titled “METHOD AND APPARATUS FOR SPECKLE NOISE REDUCTION IN ELECTROMAGNETIC INTERFERENCE DETECTION” relates to “Interference measurements obtained by comparison of a same beam (i.e. same nominal polarization, intensity, coherence length and wavelength) striking a same region on a sample at a same angle, but having a different beam wavefront upon intersection with the region are shown to provide images with independent coherent speckle noise patterns. Accordingly a plurality of interference measurements with diverse beam wavefronts can be used to identify or reduce coherent speckle noise. Reduction of the coherent speckle noise can be performed by compounding the aligned images. A change in the beam wavefront may be provided by displacing the sample in the direction of the beam between or during the measurements, when the beam is a focused beam (i.e. converging or diverging)”;
U.S. Pat. No. 8,025,410 titled “PROJECTION DEVICE PROVIDING REDUCED SPECKLE CONTRAST” describes a projection device includes a diffuser and a light source system. The light source system includes a light source, a dichroic element, an actuator, and a reflector. The light source generates a light beam that is directed to the dichroic element. The dichroic element forms first and second individual light beams from the light beam. The first individual light beam is transmitted to the diffuser. The second individual light beam is reflected from the reflector to the diffuser. The actuator is fixed to the reflector and has a removal frequency exceeding 20 Hz;
U.S. Pat. No. 7,866,831, titled “Image Projector”, describes an image projector realizing image projection with high image quality by reducing speckle noise. An image projector comprising a coherent light source, a collimation lens for transforming coherent light emitted from the coherent light source into coherent parallel light, and a projection optical system for projecting coherent parallel light is further provided with a reflection element for reflecting the coherent parallel light and capable of oscillating in parallel with the direction normal to the reflection plane, and a reflection element drive means for causing oscillatory motion of the reflection element;
U.S. Pat. No. 6,367,935 titled “METHOD AND DEVICE FOR ELIMINATING IMAGE SPECKLES IN SCANNING LASER IMAGE PROJECTION” relates to “a method for the elimination of image speckles in a scanning laser projection is suggested, in which a phase hologram is used for dividing the illumination beam of the projector into partial beams. The partial beams are heterodyned again on the image screen within the image element (pixels) to be projected in such a way that differing speckle patterns are formed which average each other out in the eye of the viewer over time and/or space. Thus, a device is provided especially for the laser projection which substantially eliminates or reduces the speckles at the viewer. However, the beam form and the beam density are hardly or not changed”;
U.S. Pat. No. 6,016,210, titled “Scatter noise reduction in holographic storage systems by speckle averaging”, describes a method and an apparatus for increasing detection signal-to-noise ratio, while reading out a hologram from a holographic storage medium, are disclosed. The hologram is written by interfering a write reference beam with an object beam. The method comprises the steps of (1) effecting multiple sequential hologram-read operations using multiple read reference beams separated from each other by a separation angle; (2) shifting the detector array contents in between hologram-read operations such that the data signal patterns incident on the detector array are approximately identical but the incident scatter noise patterns are uncorrelated; and (3) integrating the multiple hologram readouts electronically on the detector array. The apparatus comprises a laser source, a beamsteerer, a detector array and a shifting device;
U.S. Pat. No. 4,256,363 titled “SPECKLE SUPPRESSION OF HOLOGAPHIC MICROSCOPY” relates to “an apparatus for, and a method of, reconstructing and viewing a speckled holographic image through a microscope, with the result that the speckle of the holographic image is significantly reduced, without loss of resolution of the image. A finely-structured and transparent light diffuser is interposed thru the aerial image formed by a hologram or an image formed or relayed by a lens system such as a microscope objective prior to the eyepiece. This diffuser is moved in its plane with a rotary or vibratory motion to suppress the speckle”;
U.S. Pat. No. 4,155,630 titled “Speckle Elimination By Random Spatial Phase Modulation” relates to “a process and apparatus for improving image creation in a coherent light imagery system which involves directing diffused laser light onto a mirror having a rocking motion that will cause the reflected rays to sweep a two-dimensional area and focusing the reflected light through a diffuser before collimating same for use in image creation. More particularly, this invention creates the rocking motion by applying a combination of voltages to three independent piezo-electric crystals upon which the mirror is mounted”; and
An article titled: “Fresnel and Fourier digital holography architectures: a comparison” by Damien P., David S. Monaghan, Nitesh Pandey, Bryan M. Hennelly, and retrieved from the World Wide Web, at eprints(dot)nuim(dot)ie/2468/1/BH_Fresnel_Fourier(dot)pdf.
The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.